Given a curve \(\gamma :[a,b]\rightarrow M\) , we define its metric derivative (see [1]}) as
\(\left| \gamma ^{\prime } \right|_g(t):= \lim _{h\rightarrow 0}\frac{\operatorname{dist}_g\left(\gamma (t+h),\gamma (t)\right)}{\left| h \right|},\) 
